MM THE NEW EVOLUTION ®^ 



why should we find such extraordinary changes in 

 the details in successive ages? 



The answer is a simple one. While all the food 

 substances necessary for the support of animal life 

 have been available from the first, the conditions 

 under which these food substances were available have 

 varied very greatly from one epoch to another. For 

 instance, at one time the earth was largely cloud 

 enveloped. The light was relatively dim, and the 

 temperature was about the same almost everywhere. 

 The winds were light, so that the seas were calm 

 and quiet. 



Living under these conditions were representatives 

 of all the major groups we know today. But the 

 representatives of the major groups which flourished 

 at that time were quite different looking creatures 

 from the types we know at the present day. The 

 problems which they had to meet in securing food 

 and in avoiding enemies — in the struggle for existence 

 — were very different from the problems which must 

 be met by their modern representatives. A cloud 

 enshrouded world of about the same temperature 

 everywhere with only light winds and with almost 

 waveless seas is a very different thing from the world 

 of the present day. 



The changes in animal life from age to age for the 

 most part took place according to a definite plan or 

 system. A small and inconspicuous creature in one 

 age was succeeded in the next by several more spe- 

 cialized and often larger creatures, and these were suc- 

 ceeded by many still more specialized, and so on, 



